Various types of condenser installations are known, such as, for example, water-cooled surface condensers and direct-contact or jet condensers. Water-cooled surface condensers are distinguished by a multiplicity of cooling tubes, through which cooling water flows and into which the water is directed via large water chambers and on which exhaust steam flowing in from a turbine is precipitated. In this type of condenser, however, the manufacture of the cooling tubes and water chambers is expensive. Surface condensers are nowadays realized with once-through cooling or with circulation cooling, for example with a wet or dry cooling tower. In once-through cooling systems, water from a natural body of water is used open circuit as cooling medium for condensers. This type of cooling is used at sites where such fresh water is available in sufficiently large quantities at acceptable costs. In this case, the effects on the environment, such as, for example, the heating of river water, are also to be taken into account. Once-through cooling can also only be used for those condensers, such as, for example, surface condensers, in which the cooling medium does not come in direct contact with the turbine steam.
If fresh water is not available in sufficient quantity or is not a suitable cooling medium for reasons of environmental protection, various circulation circuits with recooling of the cooling medium are used. In a circulation circuit, the cooling medium flows through the condenser installation, in which it heats up due to the condensation of turbine exhaust steam and is then fed to a cooling tower for recooling and is finally pumped back to the condenser. Cooling towers are classified as wet cooling towers and dry cooling towers, the cooling medium being cooled in the former in an open system accessible to the air and in the latter in a closed system inaccessible to the air. Wet cooling towers are efficient due to the favorable heat transfer between water and air; the heat transferred leads to an evaporation of about 1 to 2% of the water flow. However, they have the known disadvantage that, due to the evaporation, they cause fog, sleet and shadows, which increasingly are becoming less acceptable in residential and farming regions. Furthermore, the evaporated water has to be replaced by fresh water. Dry cooling towers have the advantage of not causing such fog, but are less efficient compared with wet cooling towers and require an additional and complicated cooling area in the cooling tower.
Further cooling towers realized nowadays are the wet-dry cooling towers, also known as hybrid cooling towers, as described, for example, in DE 24 52 123 and in "Cutting the fog", The Chemical Engineer, Oct. 29, 1992. These cooling towers meet in particular the demands for environmental protection and the reduction in the water loss in order to avoid fog, sleet and shadows caused by the fog. To this end, the cooling water of a surface condenser is cooled in two circulations, having a dry cooling-tower part and a wet cooling-tower part. During dry cooling, the cooling water is passed through ribbed heat-exchange tubes, as a result of which the air of the dry cooling-tower part heats up by convective heat transfer. During the wet cooling, the air heats up in direct contact between air and water. Due to evaporation of the water, the air humidity increases and air saturated with water results. This saturated air mixes with the warm dry air of the dry cooling-tower part, so that a moist air flow is obtained and fog no longer develops. In order to reduce the humidity of the wet air to a practical value, approximately 20% of the heat must be given off during the dry cooling. In the hybrid cooling towers, the advantages of both cooling methods can be combined, namely the high cooling capacity of the wet method and the freedom from fog due to the dry method. In this case, the degree of hybridization, depending on the weather, can be varied by a bypass of the cooling water between dry part and wet part in order to optimize the final humidity of the air mixture.
A condensation system, also called the Heller system, is described, for example, in L. Heller and L. Forgo, "Betriebserfahrungen und weitere Entwicklungs-ergebnisse mit dem Heller-System bei Luftkondensation fur Kraftwerke", Energietechnik Dec. 13, 1963 or Grosse Kraftwerke, third volume, Springer Verlag 1968. Here, the turbine exhaust steam is condensed in a direct-contact condenser by suitable condensate, of which some of the condensate is fed to the water/steam cycle and the remainder is fed to a cooling circulation with a dry cooling tower. One of the advantages of a direct-contact condenser over a surface condenser is its very low or even zero temperature-difference rating, as a result of which the condenser pressure is reduced and the turbine power is increased. Furthermore, this type of condenser is more convenient to manufacture, since the expensive tubing in the condenser and the water chambers are omitted. Finally, no water losses occur in the dry cooling tower. However, the system has the disadvantage that a complicated heating surface is required in the dry cooling tower. In particular, this surface is larger compared with a system of the same capacity with surface condenser and wet cooling tower, since the heat transfer to the air is poorer.